The term “iron ore” is understood herein to mean mined material that includes iron oxides. The term also covers mined material that contains other valuable metals. For example, the term covers mined material that contains iron oxides and titanium oxides.
The present invention relates particularly, although by no means exclusively, to producing iron from iron ore having a gangue content of at least 5% by weight on a dry basis.
The present invention relates more particularly, although by no means exclusively, to producing iron from iron ore with minimal CO2 emissions.
Blast furnaces are the most widely-used option for producing iron from iron ore. Ironmaking and downstream steelmaking processes make a substantial contribution to CO2 emissions in the world.
At present there is no readily available substitute to carbon for the production of iron from iron ore. For example, there is no commercially-available ironmaking process that can utilise electric current in the reduction process. This means that nuclear and hydro power cannot be used as an alternate source of energy for the reduction of iron oxides to iron. As a result, sequestration of CO2 emissions is presently the most promising process for reducing CO2 emissions from the ironmaking process.
Pellets can be used in blast furnaces as a substitute for lump and sintered iron ore. Typical blast furnace pellets have less than 5% by weight of gangue. They are manufactured from low grade iron ore (i.e. iron ore with a gangue content greater than 5% by weight) that has been finely ground in order to separate the gangue material from the iron oxides. Low gangue pellets have lower coking coal consumption in blast furnaces compared with the use of higher gangue content pellets in blast furnaces. However, the use of pellets with less than 5% by weight gangue does not appreciably reduce the overall CO2 emissions of the ironmaking process due to the energy involved in grinding and producing the pellets. It should however be noted that, overall, the use of pellets as a feed stock for a blast furnace can be economic where low cost energy and low cost (high gangue) iron ores are available.
Electric arc steelmaking processes are designed to convert scrap steel to molten metal and do not offer significant opportunities for reducing CO2 emissions from the conversion of iron ores to iron in the ironmaking process. Electric arc furnaces can receive some raw materials, which typically are provided to dilute the impurities present in the scrap metal (such as copper and zinc). These raw materials must be of very low gangue content (typically less than 2% on a dry weight basis) so as not to affect the productivity of electric arc furnaces or significantly increase the electricity consumed by the furnaces (due to the increased need to heat gangue materials to the molten state).
One proposal to reduce the CO2 emissions from blast furnaces is to capture the CO2 emissions at the blast furnaces and to sequester these emissions in underground reservoirs. However, blast furnaces are fired using heated air (hot blast) and, as a result, the off-gas of a blast furnace has a high percentage of N2 which has to be stripped from the off-gas using large volume gas handling equipment before the CO2 can be sequestered. Such large volume gas handling equipment is expensive, and it is likely that it will be necessary to develop oxygen-fired blast furnaces (as alternatives to air-fired blast furnaces) before sequestration of CO2 from blast furnaces will be economically viable.
A further difficulty with sequestration of CO2 from blast furnaces arises where a blast furnace is not situated in close proximity to a suitable sequestration site. In this situation, there may be a requirement to transport the captured CO2 over thousands of kilometers of pipe line. Such pipe lines will need to be specially installed and may represent a cost to the ironmaking process that means that it is no longer economically viable.
The cost of replicating existing iron and steelmaking facilities adjacent suitable sequestration sites could, in many cases, equal or exceed the cost of installing CO2 pipelines. Moreover, simply replicating blast furnaces at suitable sequestration sites will not result in a maximum of CO2 savings as it will be necessary to solidify the molten iron to pig iron before transporting it to steelmaking facilities in other locations. This will result in additional CO2 emissions at the steelmaking facilities when the pig iron is reheated to its molten state for conversion to steel.
The above difficulties mean that an economically viable ironmaking/steelmaking process with CO2 sequestration may be difficult to achieve in practice notwithstanding that CO2 sequestration of blast furnace off-gas may itself be technically feasible.
The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.